Numerous methods have been developed over the years to produce isoprene. One method described in U.S. Pat. No. 4,524,233, herein incorporated by reference, discloses the dehydration reaction of 2-methylbutanal (2MBA) over an acid dehydration catalyst such as boron phosphate to yield isoprene. As disclosed in U.S. Pat. No. 4,524,233, a major by-product of the 2MBA dehydration is methylisopropylketone,(MIPK). For the economical operation of a process as described in this U.S. patent, it will be required to recycle the 2MBA that is not converted to MIPK or isoprene back to the dehydration reactor.
The close boiling points of 2MBA (90.degree.-92.degree. C.) and MIPK (92.degree.-94.degree. C.) will make separation by distillation difficult. Such a separation of two compounds having such a close boiling point would be known to those skilled in this art to present extreme difficulties for the efficient and economic separation of the 2MBA from the mixture.
The inventor herein has unexpectedly found that a mixture of 2MBA and MIPK can be separated to give high purity 2MBA by selectively azeotroping 2MBA with water. The resulting high purity 2MBA is easily phase separated from the azeotroping water and recycled to the dehydration reactor. None of the prior art suggests or discloses this unique discovery.